Paper detail

Cosmic anisotropies from quasars: from polarization to structural-axis alignments

The comparison of the orientations of the optical-polarization vectors of quasars that are separated by billions of light-years has led to the discovery that they are aligned instead of pointing in random directions as expected. This discovery has been confirmed and the significance of the correlations enhanced. We devoted this doctoral thesis to an in-depth analysis of these striking observations that imply Gpc-scale correlations. We developed a new and independent statistical method which is dedicated to the study and the characterization of the distribution of the orientations of vectorial quantities that are perpendicular to the lines of sight of a set of sources spread on the celestial sphere. This allowed us to confirm independently the large-scale polarization-vector alignments and to refine the limits of the alignment regions through an unbiased characterization of the signal. We also provided a detailed analysis of a large sample of polarization measurements made at radio wavelengths in which similar polarization-vector alignments are found. The regions of alignments of the quasar-radio-polarization vectors are found to be close to these of optical alignments. This might suggest that quasar axes themselves could be aligned. Based on new observations, we further analyzed the optical-polarization vectors of quasars that belong to two large groups. Taking into account the link between the optical-polarization vectors and the morphologies of the quasars, we found that the spin axes of the quasars align with the axis of the large-quasar group to which they belong. We reinforced our findings using radio-polarization data and a large sample of large-quasar groups. We additionally found that the preferred orientations of the quasar spin axes depend on the richness of their host groups.